<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>02_流程控制</title>
</head>
<body>
<script>
    //1.顺序结构
    console.log(1);
    console.log(2);
    console.log(3);
    //2.分支结构
    let username = '';
    // if (!username){
    //     alert('用户名不能为空！');
    // }else {
    //     alert('欢迎'+username+'回归！');
    // }
    //3.选择分支
    let gender = 3;
    switch (gender){
        case 1:
            console.log('男');
            break;
        case 0:
            console.log('女');
            break;
        default:
            console.log('未知');
    }
    //4.循环结构
    let names = ['张三','李四','王五'];
    for (var i = 0;i < names.length;i++){
        console.log(names[i]);
    }
    //如果用var定义变量，则i在循环结束后，仍然存在
    console.log(i);

    //增强for循环
    for (let n of names){
        console.log(n);
    }
</script>
</body>
</html>